Exhaust device of engine

ABSTRACT

A muffler in an exhaust device of an engine includes a casing, a first expansion chamber, a second expansion chamber, and a third expansion chamber separately formed in the casing, and a first communication pipe, a second communication pipe, and a third communication pipe provided in the casing. The rear exhaust pipe is connected to the first expansion chamber, the first expansion chamber communicates with the third expansion chamber via the first communication pipe, the first expansion chamber communicates with the second expansion chamber via the second communication pipe, and the second expansion chamber communicates with an outside of the casing via the third communication pipe. The third expansion chamber does not communicate with an outside of the third expansion chamber except that the third expansion chamber communicates with the first expansion chamber via the first communication pipe.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2017-251533 filed on Dec. 27, 2017, which is incorporated herein by reference in its entirety.

BACKGROUND Technical Field

The present invention relates to an exhaust device of an engine provided in a vehicle or the like.

Related Art

Generally, a vehicle or the like provided with an engine includes an exhaust pipe through which an exhaust gas from the engine flows and a muffler provided on a downstream side of the exhaust pipe. The muffler has a function to reduce exhaust noise. That is, a communication path for causing a plurality of expansion chambers and expansion chambers to communicate with one another is formed in a casing of the muffler. The exhaust gas discharged from the engine and flowing into the muffler via the exhaust pipe is expanded and attenuated in stages in the process of passing through the expansion chambers and the communication path. As a result, the exhaust noise is reduced (see, for example, JP H1-290913 A below).

SUMMARY

Enhancement of the muffler exhaust noise reduction effect is demanded with recent strengthening of the noise regulation. The muffler exhaust noise reduction effect can be enhanced with a structure in which the number of expansion chambers of the muffler is increased and the expansion and attenuation of the exhaust gas is repeated many times. However, if the number of expansion chambers is increased, the muffler is increased in size. For example, to downsize the vehicle or the like, the increase in size of the muffler is not desirable.

Further, in general, an effect to suppress a decrease in engine output can be enhanced by increasing a volume of a first-stage expansion chamber connected to an exhaust pipe in a muffler. To secure a desired engine output, increasing the volume of the first-stage expansion chamber in the muffler is demanded. However, if the volume of the first-stage expansion chamber is increased, the muffler is increased in size.

The present invention has been made in view of such a problem, and an objective of the present invention is to provide an exhaust device of an engine, the exhaust device being capable of enhancing the exhaust noise reduction effect of a muffler and suppressing a decrease in engine output while suppressing an increase in size of the muffler.

To solve the above problem, the present invention provides an exhaust device of an engine, the exhaust device including: an exhaust pipe through which an exhaust gas from the engine flows; and a muffler provided on a downstream side of the exhaust pipe, the muffler including a casing, a first expansion chamber, a second expansion chamber, and a third expansion chamber separately formed in the casing, and a first communication pipe, a second communication pipe, and a third communication pipe provided in the casing, wherein the exhaust pipe is connected to the first expansion chamber, the first expansion chamber communicates with the third expansion chamber via the first communication pipe, the first expansion chamber communicates with the second expansion chamber via the second communication pipe, the second expansion chamber communicates with, via the third communication pipe, another chamber separately formed from any of the first expansion chamber, the second expansion chamber, and the third expansion chamber outside or inside the casing, and the third expansion chamber does not communicate with an outside of the third expansion chamber except that the third expansion chamber communicates with the first expansion chamber via the first communication pipe.

According to the present invention, the exhaust noise reduction effect of the muffler can be enhanced and the decrease in engine output can be suppressed while the increase in size of the muffler can be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram illustrating a motorcycle provided with an exhaust device of a first embodiment of the present invention;

FIG. 2 is an external view illustrating a muffler and the like in the exhaust device of the first embodiment of the present invention;

FIG. 3 is a sectional view illustrating the muffler as viewed from the direction of arrows in FIG. 2;

FIG. 4 is a sectional view illustrating the muffler as viewed from the direction of arrows IV-IV in FIG. 3;

FIG. 5 is a sectional view illustrating the muffler as viewed from the direction of arrows V-V in FIG. 3;

FIG. 6 is an explanatory view schematically illustrating a structure of the muffler in the exhaust device of the first embodiment of the present invention;

FIG. 7 is an external view illustrating a muffler and the like in an exhaust device of a second embodiment of the present invention;

FIG. 8 is a sectional view illustrating the muffler as viewed from the directions of arrows VIII-VI It in FIG. 7;

FIG. 9 is a sectional view illustrating the muffler as viewed from the direction of arrows IX-IX in FIG. 8;

FIG. 10 is a sectional view illustrating the muffler as viewed from the direction of arrows X-X in FIG. 8; and

FIG. 11 is a sectional view illustrating the muffler as viewed from the direction of arrows XI-XI in FIG. 8.

DETAILED DESCRIPTION

An exhaust device according to an embodiment of the present invention includes an exhaust pipe through which an exhaust gas from an engine flows, and a muffler provided on a downstream side of the exhaust pipe. The muffler includes a casing, a first expansion chamber, a second expansion chamber, and a third expansion chamber separately formed in the casing, and a first communication pipe, a second communication pipe, and a third communication pipe provided in the casing.

The exhaust pipe is connected to the first expansion chamber. The first expansion chamber communicates with the third expansion chamber via the first communication pipe, and communicates with the second expansion chamber via the second communication pipe. The second expansion chamber communicates with an outside of the casing via the third communication pipe. Note that, in the casing, another chamber may be separately formed from any of the first expansion chamber, the second expansion chamber, and the third expansion chamber, and the second expansion chamber may communicate with the another chamber, instead of the outside of the casing, via the third communication pipe. The third expansion chamber does not communicate with an outside of the third expansion chamber except that the third expansion chamber communicates with the first expansion chamber via the first communication pipe.

The muffler of the exhaust device of the present embodiment has the structure in which the exhaust pipe is connected to the first expansion chamber, the first expansion chamber communicates with the third expansion chamber via the first communication pipe, and the third expansion chamber does not communicate with the outside of the third expansion chamber except that the third expansion chamber communicates with the first expansion chamber via the first communication pipe, whereby the first expansion chamber, the third expansion chamber, and the first communication pipe as a whole can be caused to function as a first-stage expansion chamber to which the exhaust pipe is connected.

As described above, a decrease in engine output can be enhanced by increasing the volume of the first-stage expansion chamber to which the exhaust pipe is connected in the muffler. In the muffler of the exhaust device of the present embodiment, a total of the volumes of the first expansion chamber, the third expansion chamber, and the first communication pipe is the volume of the first-stage expansion chamber. Therefore, the volume of the first-stage expansion chamber can be increased on the whole by increasing the volume of the first expansion chamber, increasing the volume of the third expansion chamber, or increasing the volume of the first communication pipe (increasing the length of the first communication pipe, for example). The first expansion chamber, the third expansion chamber, and the first communication pipe can be dispersed in the casing of the muffler in such a manner that the first expansion chamber is arranged in the rear in the casing, and the third expansion chamber is arranged in the front in the casing. Therefore, the volume of the first-stage expansion chamber in the muffler of the present embodiment can be increased while suppressing the increase in size of the muffler on the whole by selecting one or ones of the first expansion chamber, the third expansion chamber, and the first communication pipe, the volume or volumes of which can be increased, while suppressing the increase in size of the muffler, and increasing the volume or volumes, while taking the structural restrictions of the muffler into consideration, for example. Therefore, both the suppression of the increase in size of the muffler and the suppression of the decrease in engine output can be achieved.

Further, in the structure in which the first expansion chamber and the third expansion chamber are connected with the first communication pipe, the exhaust gas is attenuated when flowing in from the first expansion chamber or the third expansion chamber to the first communication pipe, and is expanded when flowing out from the first communication pipe to the third expansion chamber or the first expansion chamber. In this manner, the exhaust noise reduction effect can be enhanced with the structure that functions as the first-stage expansion chamber in the muffler of the present embodiment. Therefore, the exhaust noise reduction effect can be sufficiently enhanced by simply providing the second expansion chamber in addition to the first expansion chamber and the third expansion chamber that function as the first-stage expansion chamber, and a large number of expansion chambers is not necessary to obtain high exhaust noise reduction effect. Therefore, both the suppression of the increase in size of the muffler and the improvement of the exhaust noise reduction effect can be achieved.

First Embodiment

FIG. 1 illustrates a motorcycle 1 provided with an exhaust device 8 of a first embodiment of the present invention. Note that arrows respectively representing the front (F), rear (B), up (U), down (D), right (R), and left (L) are drawn as needed at the lower right in each of the drawings. When a direction is described in each embodiment, the direction follows these arrows.

In FIG. 1, a front wheel 4 is rotatably supported on a front portion of a vehicle body frame 2 of the motorcycle 1 via a front fork 3. Further, a rear wheel 6 is rotatably supported on a rear portion of the vehicle body frame 2 via a swing arm 5. Further, an engine 7 is supported on an intermediate portion in a front-rear direction of the vehicle body frame 2. The exhaust device 8 of the present embodiment is provided in a portion from a lower side of the engine 7 to a right side of the rear wheel 6 in the motorcycle 1.

The exhaust device 8 is a device that discharges an exhaust gas of the engine 7 to the atmosphere. The exhaust device 8 includes a front exhaust pipe 11, a chamber 12, a catalyst device 13, a rear exhaust pipe 14, and a muffler 15.

The front exhaust pipe 11 is a metal-made pipe connecting an exhaust port of the engine 7 and the chamber 12, and sends the exhaust gas discharged through the exhaust port to the chamber 12. The chamber 12 is provided on a lower side of the engine 7. An expansion chamber is formed in the chamber 12, and the exhaust gas sent from the front exhaust pipe 11 flows through this expansion chamber. The catalyst device 13 is a device that reduces harmful substances contained in the exhaust gas, and is provided on an upstream side or a downstream side of the expansion chamber in the chamber 12, for example. The rear exhaust pipe 14 is a metal-made pipe connecting the chamber 12 and the muffler 15, and sends the exhaust gas flowing out of the chamber 12 to the muffler 15. The muffler 15 is provided on a right side of the rear wheel 6. As will be described below, the exhaust gas sent from the rear exhaust pipe 14 flows through a plurality of expansion chambers provided in the muffler 15 and is then discharged to the atmosphere. In the exhaust device 8 of the present embodiment, exhaust noise is reduced by the chamber 12 and the muffler 15.

FIG. 2 illustrates a downstream side of the rear exhaust pipe 14 and the muffler 15 in the exhaust device 8. FIG. 3 illustrates a cross section of the muffler 15 as viewed from the direction of arrows in FIG. 2. FIG. 4 illustrates a longitudinal section of the muffler 15 as viewed from the direction of arrows IV-IV in FIG. 3, and FIG. 5 illustrates a longitudinal section of the muffler 15 as viewed from the direction of arrows V-V in FIG. 3.

As illustrated in FIGS. 2 to 5, the muffler 15 includes a casing 21, a first expansion chamber R1, a second expansion chamber R2, and a third expansion chamber R3 separately formed in the casing 21, and a first communication pipe 31, a second communication pipe 32, and a third communication pipe 33 provided in the casing 21.

Specifically, as illustrated in FIG. 1, the casing 21 is formed in a cylindrical shape long in an axial direction and is arranged such that an axis X the casing 21 faces from a front lower side to a rear upper side in a right-side region of the rear wheel 6 of the motorcycle 1. Further, as illustrated in FIG. 2, the casing 21 includes a casing body 22 formed in a cylindrical shape. As illustrated in FIG. 3, the casing body 22 has a double cylinder structure including an outer cylinder 23 and an inner cylinder 24. Further, as illustrated in FIG. 4, a front lid portion 25 is provided on a front end portion of the casing body 22, and an opening in a front end of the casing body 22 is closed by the front lid portion 25. Further, a hole portion 25A for allowing the downstream side of the rear exhaust pipe 14 to be inserted into the casing 21 is formed in the front lid portion 25. Further, a rear lid portion 26 is provided on a rear end portion of the casing body 22, and an opening in a rear end of the casing body 22 is closed by the rear lid portion 26. Further, a hole portion 26A for allowing the third communication pipe 33 described below to pass through is formed in the rear lid portion 26. Further, a cover 27 is attached to the rear lid portion 26, and a hole portion 27A for allowing the third communication pipe 33 to pass through is also formed in the cover 27. These portions of the casing 21 are formed of a metal material such as stainless steel, iron, or titanium, and are joined by means such as welding or screwing.

Further, as illustrated in FIG. 4, the first expansion chamber R1, the second expansion chamber R2, and the third expansion chamber R3 are formed in the casing 21. That is, a rear partition plate 28 and a front partition plate 29 are provided in the casing 21, and a columnar space in the casing 21 is divided into three spaces by the rear partition plate 28 and the front partition plate 29. Then, of the three spaces, the rearmost space serves as the first expansion chamber R1, the intermediate space in the front-rear direction serves as the second expansion chamber R2, and the frontmost space serves as the third expansion chamber R3. In other words, in the casing 21, the first expansion chamber R1 is formed closest to an outlet side, the third expansion chamber R3 is formed closest to an inlet side, and the second expansion chamber R2 is formed between the first expansion chamber R1 and the third expansion chamber R3.

The rear partition plate 28 and the front partition plate 29 are formed of, for example, a metal material in a disk shape or a cylindrical shape short in the axial direction with a lid. In the present embodiment, the rear partition plate 28 is arranged at a rear position with respect to an intermediate portion in the front-rear direction in the casing body 22. Specifically, the rear partition plate 28 is arranged at a front position from a rear end of the casing body 22 by about a quarter of the entire length of the casing body 22. Further, the front partition plate 29 is arranged near the intermediate portion in the front-rear direction in the casing body 22, specifically, at a slightly front position with respect to the intermediate portion in the front-rear direction. Further, the rear partition plate 28 and the front partition plate 29 are fixed to an inner peripheral surface of the inner cylinder 24 by means of welding or screwing. Further, an insertion hole 28A for allowing the rear exhaust pipe 14 to pass through, an insertion hole 28B for allowing the first communication pipe 31 to pass through, an insertion hole 28C for allowing the second communication pipe 32 to pass through, and an insertion hole 28D for allowing the third communication pipe 33 to pass through are formed in the rear partition plate 28. Further, an insertion hole 29A for allowing the rear exhaust pipe 14 to pass through, and an insertion hole 29B for allowing the first communication pipe 31 to pass through are formed in the front partition plate 29.

The downstream side of the rear exhaust pipe 14 is connected to the first expansion chamber R1. That is, the rear exhaust pipe 14 extends rearward from the chamber 12, and a rear end side (downstream side) of the rear exhaust pipe 14 is inserted into the casing 21 through the hole portion 25A formed in the front lid portion 25 of the muffler 15, as illustrated in FIG. 4. Further, the rear end side of the rear exhaust pipe 14 linearly extends rearward parallel to the axis X of the casing 21 in the casing 21, and enters the first expansion chamber R1 from the hole portion 25A across the third expansion chamber R3 and the second expansion chamber R2. Then, an opening portion in a rear end of the rear exhaust pipe 14 opens to the first expansion chamber R1. Further, the rear end side of the rear exhaust pipe 14 is inserted into the insertion hole 29A in the front partition plate 29 and the insertion hole 28A in the rear partition plate 28 and is supported by the front partition plate 29 and the rear partition plate 28 in the casing 21. Further, as illustrated in FIG. 3, the rear exhaust pipe 14 is arranged at a position close to the inner peripheral surface of the inner cylinder 24 with respect to a center of the casing 21, where the axis X of the casing 21 passes through, specifically, at a lower side of the center of the casing 21, in the casing 21. Further, the rear end side of the rear exhaust pipe 14 is formed in a linearly extending cylindrical shape, and the shape of an opening portion in the rear end is substantially a perfect circle.

As illustrated in FIG. 5, the first communication pipe 31 connects the first expansion chamber R1 and the third expansion chamber R3 in the casing 21, and the first expansion chamber R1 communicates with the third expansion chamber R3 via the first communication pipe 31. The first communication pipe 31 is a metal-made pipe formed in a tubular shape having a substantially perfect circular shape in cross section. The first communication pipe 31 linearly extends parallel to the axis X of the casing 21 between the first expansion chamber R1 and the third expansion chamber R3 across the second expansion chamber R2. Further, an inner diameter of the first communication pipe 31 is constant from a front end to a rear end of the first communication pipe 31. Further, a rear end side of the first communication pipe 31 enters the first expansion chamber R1, and an opening portion in a rear end of the first communication pipe 31 open to the first expansion chamber R1. Further, in the present embodiment, the rear end side of the first communication pipe 31 enters up to a vicinity of an intermediate portion in the front-rear direction in the first expansion chamber R1. Meanwhile, a front end side of the first communication pipe 31 enters the third expansion chamber R3, and an opening portion in a front end of the first communication pipe 31 opens to the third expansion chamber R3. Further, in the present embodiment, a front end side of the first communication pipe 31 enters up to a vicinity of an intermediate portion in the front-rear direction in the third expansion chamber R3. Further, the first communication pipe 31 is inserted into the insertion hole 29B in the front partition plate 29 and the insertion hole 28B in the rear partition plate 28 and is supported by the front partition plate 29 and the rear partition plate 28 in the casing 21. Further, in the present embodiment, the length of the first communication pipe 31 is set to a value larger than half of the entire length of the casing body 22, for example.

Further, as illustrated in FIG. 3, the first communication pipe 31 is arranged on the center side of the casing 21 with respect to the rear exhaust pipe 14 in the casing 21. Further, a sectional area (opening area) of a flow path of the first communication pipe 31 is set to be equal to or larger than a sectional area (an opening area of the rear end) of a flow path on the rear end side of the rear exhaust pipe 14. Further, the inner diameter of the first communication pipe 31 is set to be equal to or larger than an inner diameter of the rear exhaust pipe 14. Note that the sectional area of the flow path of the first communication pipe 31 is significantly smaller than respective inner diameters of the first expansion chamber R1 and the third expansion chamber R3.

As illustrated in FIG. 4, the second communication pipe 32 connects the first expansion chamber R1 and the second expansion chamber R2 in the casing 21, and the first expansion chamber R1 communicates with the second expansion chamber R2 via the second communication pipe 32. The second communication pipe 32 is a metal-made pipe formed in a tubular shape having a substantially perfect circular shape in cross section. The second communication pipe 32 linearly extends parallel to the axis X of the casing 21 between the first expansion chamber R1 and the second expansion chamber R2. An inner diameter of the second communication pipe 32 is constant from a front end to a rear end of the second communication pipe 32. Further, a rear end side of the second communication pipe 32 enters the first expansion chamber R1, and an opening portion in a rear end of the second communication pipe 32 opens to the first expansion chamber R1. Further, in the present embodiment, the rear end of the second communication pipe 32 is located on a rear side with respect to the rear end of the first communication pipe 31 in the first expansion chamber R1. Meanwhile, a front end side of the second communication pipe 32 enters the second expansion chamber R2, and an opening portion in a front end of the second communication pipe 32 opens to the second expansion chamber R2. Further, in the present embodiment, the front end side of the second communication pipe 32 enters up to a vicinity of an intermediate portion in the front-rear direction in the second expansion chamber R2. Further, the second communication pipe 32 is inserted into the insertion hole 28C in the rear partition plate 28 and is supported by the rear partition plate 28 in the casing 21. Further, the second communication pipe 32 is shorter than the first communication pipe 31.

Further, as illustrated in FIG. 3, the second communication pipe 32 is arranged on an upper side of the center of the casing 21 in the casing 21. Further, the second communication pipe 32 is roughly arranged on an opposite side of the rear exhaust pipe 14 across the first communication pipe 31. Further, a sectional area (opening area) of a flow path of the second communication pipe 32 is set to be less than the sectional area (opening area) of the flow path on the rear end side of the rear exhaust pipe 14, and is set to be less than the sectional area (opening area) of the flow path of the first communication pipe 31. Further, the inner diameter of the second communication pipe 32 is set to be less than an inner diameter of the rear exhaust pipe 14, and is set to be less than the inner diameter of the first communication pipe 31.

As illustrated in FIG. 5, the third communication pipe 33 has a front end side connected to the second expansion chamber R2 in the casing 21 and has a rear end side extend outward from the casing 21. As a result, the second expansion chamber R2 communicates with the outside of the casing 21 via the third communication pipe 33. The third communication pipe 33 is a metal-made pipe formed in a tubular shape having a substantially perfect circular shape in cross section. The third communication pipe 33 extends outward from the second expansion chamber R2 to the outside of the casing 21 across the first expansion chamber R1. A front portion of the third communication pipe 33 linearly extends parallel to the axis X of the casing 21, and a rear portion of the third communication pipe 33 is gently curved downward. Further, an inner diameter of the third communication pipe 33 is constant from the front end to the rear end of the third communication pipe 33. Further, the front end side of the third communication pipe 33 enters the second expansion chamber R2, and an opening portion in a front end of the third communication pipe 33 opens to the second expansion chamber R2. Further, in the present embodiment, the front end of the third communication pipe 33 is located on a front side with respect to the front end of the second communication pipe 32 in the second expansion chamber R2. Meanwhile, the rear end side of the third communication pipe 33 passes through the hole portion 26A formed in the rear lid portion 26 and the hole portion 27A formed in the cover 27 and extends up to a position facing the outside of the casing 21, and an opening portion in the rear end of the third communication pipe 33 opens to the outside of the casing 21. Further, the third communication pipe 33 is inserted into the insertion hole 28D in the rear partition plate 28 and the hole portion 26A in the rear lid portion 26 and is supported by the rear partition plate 28 and the rear lid portion 26.

Further, as illustrated in FIG. 3, the third communication pipe 33 is arranged on an upper side of the center of the casing 21 in the casing 21. Further, the third communication pipe 33 is roughly arranged on an opposite side of the rear exhaust pipe 14 across the first communication pipe 31. Further, a sectional area (opening area) of a flow path of the third communication pipe 33 is set to be equal to or smaller than the sectional area (opening area) of the flow path of the second communication pipe 32. Further, the inner diameter of the third communication pipe 33 is set to be equal to or smaller than the inner diameter of the second communication pipe 32.

FIG. 6 schematically illustrates a structure of the muffler 15 in the exhaust device 8 of the present embodiment described in detail. The muffler 15 has the following structural characteristics. That is, as illustrated in FIG. 6, in the first expansion chamber R1, the rear exhaust pipe 14 serves as an inflow path of the exhaust gas and the second communication pipe 32 serves as an outflow path of the exhaust gas. As described above, the first expansion chamber R1 has the inflow path of the exhaust gas and the outflow path of the exhaust gas, which are different from each other. Further, in the second expansion chamber R2, the second communication pipe 32 serves as an inflow path of the exhaust gas and the third communication pipe 33 serves as an outflow path of the exhaust gas. As described above, the second expansion chamber R2 has the inflow path of the exhaust gas and the outflow path of the exhaust gas, which are different from each other. In contrast, the pipe connected to the third expansion chamber R3 is the first communication pipe 31 only. That is, the third expansion chamber R3 does not communicate with the outside of the third expansion chamber R3 except that the third expansion chamber R3 communicates with the first expansion chamber R1 via the first communication pipe 31. Therefore, in the third expansion chamber R3, the first communication pipe 31 serves as an inflow path of the exhaust gas and also serves as an outflow path of the exhaust gas. Further, the sectional area of the flow path of the first communication pipe 31 connecting the first expansion chamber R1 and the third expansion chamber R3 is equal to or larger than the opening area in the rear end of the rear exhaust pipe 14 and is larger than the sectional area of the flow path of the second communication pipe 32. With such a structure, a combination of the first expansion chamber R1, the third expansion chamber R3, and the first communication pipe 31 in the muffler 15 as a whole similarly functions to the first-stage expansion chamber to which the exhaust pipe is connected in the typical muffler. Rc in FIG. 6 functionally illustrates the first-stage expansion chamber formed by the first expansion chamber R1, the third expansion chamber R3, and the first communication pipe 31.

According to the muffler 15 in the present embodiment having such structural characteristics, the exhaust noise reduction effect can be enhanced while the increase in size of the muffler 15 is suppressed.

That is, as illustrated in FIG. 6, the exhaust gas flowing out of the chamber 12 passes through the rear exhaust pipe 14 and flows into the first-stage expansion chamber Rc in the muffler 15. Then, expansion of the exhaust gas and interference of a pressure wave in the exhaust gas occur in the first-stage expansion chamber Rc. Further, when the pressure in the second expansion chamber R2 is lower than the pressure in the first-stage expansion chamber Rc, the exhaust gas flows from the first-stage expansion chamber Rc through the second communication pipe 32 into the second expansion chamber R2. Then, the expansion of the exhaust gas and the interference of the pressure wave in the exhaust gas occur in the second expansion chamber R2. Further, the exhaust gas in the second expansion chamber R2 flows out to the outside of the casing 21 through the third communication pipe 33. The exhaust noise is reduced by the expansion and interference of the exhaust gas occurring in the first-stage expansion chamber Rc and the second expansion chamber R2, and attenuation of the pressure wave of the exhaust gas occurring when the exhaust gas passes through the second communication pipe 32 or the third communication pipe 33, and the like.

Furthermore, in the muffler 15 of the present embodiment, the first-stage expansion chamber Rc is functionally formed by the first expansion chamber R1, the third expansion chamber R3, and the first communication pipe 31 as a whole. In this first-stage expansion chamber Rc, the exhaust gas flowing through the rear exhaust pipe 14 first flows into the first expansion chamber R1, most of the exhaust gas flows through the first communication pipe 31 having the largest sectional area of the flow path, of the communication pipes opening to the first expansion chamber R1, into the third expansion chamber R3. Thereafter, the exhaust gas is moved between the third expansion chamber R3 and the first expansion chamber R1 via the first communication pipe 31 due to a difference in pressure between the first expansion chamber R1 and the third expansion chamber R3. Such a flow of the exhaust gas in the first-stage expansion chamber Rc causes the expansion, interference, or attenuation of the exhaust gas. Thereby, the exhaust noise is reduced.

According to the muffler 15 in the present embodiment, the exhaust noise reduction effect can be enhanced by the first expansion chamber R1 and the third expansion chamber R3 that form the first-stage expansion chamber Rc, and the second expansion chamber R2. That is, a large number of the expansion chambers are not required to enhance the exhaust noise reduction effect. Therefore, the exhaust noise reduction effect can be enhanced while the increase in size of the muffler 15 is suppressed.

Further, according to the muffler 15 having the above-described structural characteristics, the decrease in engine output can be suppressed and desired engine output can be secured while the increase in size of the muffler 15 is suppressed.

That is, in general, the effect to suppress the decrease in engine output is enhanced when the volume of the first-stage expansion chamber to which the exhaust pipe is connected is increased in the muffler. In the muffler 15 of the present embodiment, the first-stage expansion chamber Rc is functionally formed by the first expansion chamber R1, the third expansion chamber R3, and the first communication pipe 31 as a whole. Therefore, the volume of the first-stage expansion chamber Rc is a value of a total of the respective volumes of the first expansion chamber R1, the third expansion chamber R3, and the first communication pipe 31. Therefore, the volume of the first-stage expansion chamber Rc can be increased by increasing the volume of the first expansion chamber R1, increasing the volume of the third expansion chamber R3, or increasing the volume of the first communication pipe 31 (increasing the length of the first communication pipe 31, for example). Since the first expansion chamber R1, the third expansion chamber R3, and the first communication pipe 31 are dispersed in the casing 21 of the muffler 15, the volume of the first-stage expansion chamber Rc can be increased while the increase in size of the muffler 15 is suppressed, by selecting one or ones of the first expansion chamber R1, the third expansion chamber R3, and the first communication pipe 31, the volume or volumes of which can be increased, while suppressing the increase in size of the muffler 15, and increasing the volume or volumes, while taking the structural restrictions of the muffler 15 (for example, arrangement of another expansion chamber) or the structural restrictions of the motorcycle 1 (for example, arrangement of other parts in a rear portion of the motorcycle 1) into consideration, for example. Therefore, the decrease in engine output can be suppressed and desired engine output can be secured while the increase in size of the muffler 15 is suppressed.

Further, in the casing 21 of the muffler 15 of the present embodiment, the second expansion chamber R2 is arranged between the first expansion chamber R1 and the third expansion chamber R3. With such an arrangement, the first expansion chamber R1 and the third expansion chamber R3 can be separated from each other, and the length of the first communication pipe 31 can be increased. The volume of the first-stage expansion chamber Rc can be increased by increasing the length of the first communication pipe 31. Therefore, the effect to suppress a decrease in engine output can be enhanced.

Further, the long first communication pipe 31 can be provided without extending the casing 21 by arranging the second expansion chamber R2 between the first expansion chamber R1 and the third expansion chamber R3, and providing the first communication pipe 31 across the second expansion chamber R2.

Further, in the casing 21 of the muffler 15 of the present embodiment, the first expansion chamber R1 is arranged on the rear side of the third expansion chamber R3. With such an arrangement, the first expansion chamber R1 can be separated from the engine 7 while the entire casing 21 as a whole is brought close to the engine 7. As a result, the engine 7 and the muffler 15 can be arranged close to each other, and at the same time, the exhaust pipe connecting the engine 7 and the first expansion chamber R1, more specifically, the rear exhaust pipe 14 connecting the chamber 12 and the first expansion chamber R1 can be made long.

Further, in the muffler 15 of the present embodiment, the first expansion chamber R1 is arranged in a rearmost part of the casing 21, and the third expansion chamber R3 is arranged in a frontmost part of the casing 21. By arranging the first expansion chamber R1 in the rearmost part in the casing 21, the engine 7 and the muffler 15 can be arranged close to each other, and the effect to increase the length of the rear exhaust pipe 14 can be further enhanced. Further, the length of the first communication pipe 31 connecting the first expansion chamber R1 and the third expansion chamber R3 can be further increased, and the effect to increase the volume of the first-stage expansion chamber Rc and suppress the decrease in the engine output can be further enhanced, by respectively arranging the first expansion chamber R1 and the third expansion chamber R3 in the rearmost part and the frontmost part in the casing 21.

Further, the opening area of the rear end opening to the first expansion chamber R1 in the first communication pipe 31 of the muffler 15 of the present embodiment, is equal to or larger than the opening area of the rear end opening to the first expansion chamber R1 in the rear exhaust pipe 14. Thereby, the resistance of the exhaust gas flowing from the first expansion chamber R1 to the third expansion chamber R3 via the first communication pipe 31 can be made small. Therefore, a rise of pressure (back pressure) on the exhaust side of the engine 7 can be suppressed, and the decrease in engine output can be suppressed.

Further, in the casing 21 of the muffler 15 of the present embodiment, the rear exhaust pipe 14 is arranged at the position close to the inner peripheral surface of the inner cylinder 24 with respect to the center of the casing 21, the first communication pipe 31 is arranged on the center side of the casing 21 with respect to the rear exhaust pipe 14, and the second communication pipe 32 and the third communication pipe 33 are roughly arranged on the opposite side of the rear exhaust pipe 14 across the first communication pipe 31. With the arrangement, wasteful detouring of the exhaust gas in the casing 21 can be suppressed. Therefore, an effect to suppress the rise of the back pressure of the engine 7 can be enhanced.

Second Embodiment

FIG. 7 illustrates a downstream side of a rear exhaust pipe 54 and a muffler 55 in an exhaust device of a second embodiment of the present invention. FIG. 8 illustrates a cross section of the muffler 55 as viewed from the directions of arrows VIII-VIII in FIG. 7. FIG. 9 illustrates a longitudinal section of the muffler 55 as viewed from the direction of arrows IX-IX in FIG. 8, FIG. 10 illustrates a longitudinal section of the muffler 55 as viewed from the direction of arrows X-X in FIG. 8, and FIG. 11 illustrates a longitudinal section of the muffler 55 as viewed from the direction of arrows XI-XI in FIG. 8. Note that, in the exhaust device of the second embodiment of the present invention, the same constituent element as the exhaust device 8 of the first embodiment of the present invention is denoted by the same reference numeral and description of the constituent element is omitted.

In an exhaust device 8 of the present embodiment, as illustrated in FIG. 9, a catalytic device 53 is provided in a portion located in a casing 21 of the muffler 55 on a downstream side of the rear exhaust pipe 54. Further, as illustrated in FIG. 10, two first communication pipes 61A and 61B are provided in the casing 21. These first communication pipes 61A and 61B are arranged in parallel between a first expansion chamber R1 and a third expansion chamber R3, and the first expansion chamber R1 and the third expansion chamber R3 are connected by first communication pipes 61A and 61B. Further, as illustrated in FIG. 8, in the casing 21, the rear exhaust pipe 54 is arranged on a lower left side of a center of the casing 21, through which an axis X of the casing 21 passes, the one first communication pipe 61A is arranged on a upper right side of the center of the casing 21, and the other first communication pipe 61B is arranged on a upper left side of the center of the casing 21. Further, a second communication pipe 32 is arranged on a lower right side of the center of the casing 21, and a third communication pipe 33 is arranged on an upper side of the center of the casing 21. Further, a total of a sectional area (opening area) of a flow path of the one first communication pipe 61A and a sectional area (opening area) of a flow path of the other first communication pipe 61B is equal to or larger than the opening area in the rear end of the rear exhaust pipe 14. Further; the sectional area (opening area) of the flow path of at least one of the first communication pipes 61A and 61B is larger than a sectional area (opening area) of a flow path of the second communication pipe 32.

According to the muffler 55 in the present embodiment having such a configuration, functions and effects similar to those of the muffler 15 in the first embodiment of the present invention can be obtained. Further, according to the muffler 55 in the present embodiment, the configuration is provided with the two first communication pipes 61A and 61B, whereby the muffler 55 can be downsized. That is, in the case of providing a single thick first communication pipe having a desired flow path sectional area in the casing 21, a large space in one place needs to be secured in the casing 21. In contrast, in the case of providing the two first communication pipes 61A and 61B having the desired flow path sectional area as the total flow path sectional area in the casing 21, relatively small two spaces are provided in the casing 21 in a dispersed manner. Therefore, the cross-sectional area of the casing 21 can be made small, and the muffler 55 can be downsized.

Note that, as described in each of the above embodiments, in the muffler 15 (55), the muffler 15 can be downsized by arranging the second expansion chamber R2 between the first expansion chamber R1 and the third expansion chamber R3. However, the arrangement (the direction of the arrangement, the arrangement order, or the like) of the first expansion chamber R1, the second expansion chamber R2, and the third expansion chamber R3 is not limited to the expansion. Further, the ratio of the respective volumes of the first expansion chamber R1, the second expansion chamber R2, and the third expansion chamber R3 is not limited to that illustrated in FIG. 4 and the like. Further, the respective positions of the front partition plate 29 and the rear partition plate 28 in the front-rear direction in the casing 21 are not limited to those illustrated in FIG. 4 and the like. Further, another chamber independent of any of the first expansion chamber R1, the second expansion chamber R2, and the third expansion chamber R3 may be added in the casing 21, and the downstream side of the third communication pipe 33 may be connected to the another chamber. Further, the third expansion chamber R3 may be formed in a casing different from a casing in which the first expansion chamber R1 and the second expansion chamber R2 are formed, and these two casings may be connected by the first communication pipe 31.

Further, the number of the first communication pipes 31 may be three or more. Further, the number of the second communication pipes 32 or the third communication pipes 33 may be two or more. Further, the shape of the cross section of each communication pipe is not limited to the perfect circle, and may be another shape such as an elliptical shape. Further, the shape of the cross section of the casing 21 is not limited to the perfect circle, and may be another shape such as an elliptical shape, a quadrangular shape, or a triangular shape. Further, the position at which the muffler 15 is provided in the motorcycle 1 is not limited to the position illustrated in FIG. 1.

Further, in the second embodiment of the present invention, the sectional area (opening area) of the flow path of at least one of the two first communication pipes 61A and 61B may be made equal to or larger than the opening area in the rear end of the rear exhaust pipe 14. Thereby, the exhaust gas can be easily moved between the first expansion chamber R1 and the third expansion chamber R3.

Further, the present invention can also be applied to an exhaust device without a chamber or an exhaust device without a catalyst device. Further, application of the exhaust device of the present invention is not limited to motorcycles, and the exhaust device of the present invention can also be applied to other types of saddled vehicles such as a three-wheeled motor vehicle, other types of vehicles such as a four-wheeled motor vehicle, and types other than vehicles such as an outboard motor.

Further, the present invention can be appropriately changed within a scope not contrary to the gist or idea of the invention that can be read from the claims and the entire specification, and the exhaust device of the engine accompanied by such change is also included in the technical idea of the present invention. 

What is claimed is:
 1. An exhaust device of an engine, the exhaust device comprising: an exhaust pipe through which an exhaust gas from the engine flows; and a muffler provided on a downstream side of the exhaust pipe, the muffler including a casing, a first expansion chamber, a second expansion chamber, and a third expansion chamber separately formed in the casing, and a first communication pipe, a second communication pipe, and a third communication pipe provided in the casing, wherein the exhaust pipe is connected to the first expansion chamber, the first expansion chamber communicates with the third expansion chamber via the first communication pipe, the first expansion chamber communicates with the second expansion chamber via the second communication pipe, the second expansion chamber communicates with, via the third communication pipe, another chamber separately formed from any of the first expansion chamber, the second expansion chamber, and the third expansion chamber outside or inside the casing, and the third expansion chamber does not communicate with an outside of the third expansion chamber except that the third expansion chamber communicates with the first expansion chamber via the first communication pipe.
 2. The exhaust device of an engine according to claim 1, wherein the second expansion chamber is arranged between the first expansion chamber and the third expansion chamber in the casing.
 3. The exhaust device of an engine according to claim 2, wherein the muffler is provided on a rear side of the engine in a vehicle provided with the engine, the casing has a shape long in a front-rear direction of the vehicle, and the first expansion chamber is arranged on a rear side of the third expansion chamber in the casing.
 4. The exhaust device of an engine according to claim 3, wherein the first expansion chamber is arranged in a rearmost part in the casing, and the third expansion chamber is arranged in a frontmost part in the casing.
 5. The exhaust device of an engine according to claim 1, wherein an opening area of an end portion opening to the first expansion chamber in the first communication pipe is equal to or larger than an opening area of an end portion opening to the first expansion chamber in the exhaust pipe.
 6. The exhaust device of an engine according to claim 1, wherein the first communication pipe is one of a plurality of first communication pipes, and the muffler includes the plurality of the first communication pipes.
 7. The exhaust device of an engine according to claim 6, wherein a total of opening areas of end portions opening to the first expansion chamber in the plurality of first communication pipes is equal to or larger than an opening area of an end portion opening to the first expansion chamber in the exhaust pipe. 